Announcement

Collapse
No announcement yet.

Dell E171FPb No Backlight - Test Inverter?

Collapse
X
Collapse
 
  • Page of 1
  • Filter
  • Time
  • Show
Clear All
new posts
Previous template Next
    #1

    Dell E171FPb No Backlight - Test Inverter?

    To cut right to the point:
    Is there a way I can tell if the problem is the inverter before buying a new one? The inverter is getting 25VDC, and the SMT fuse is fine. I don't measure any voltage going to the lamps, what should this voltage be? There are 2 conductors coming from the logic board that I assume are an on/off signal; any way to "jump" these on so I can be sure the problem isn't just a lack of this signal? Got a few old laptops laying around, could I harvest an inverter from one of these?

    Long Version:
    I have a Dell 17" display that has been acting up and getting worse, seemingly bad caps. It would take a long time (eventually hours) to start up and even the power led would come on for usually just a split second before going off. During this extended power on phase I would get a bit of light flickering.

    Well I replaced all the 1000uF caps, and it started to act normally except no backlight. Replaced the 2 caps on the inverter board, one of which was bulged a bit, and still no joy. I do get 25VDC to the inverter board (and through the little SMT fuse on it), which seems right as this is what the caps were rated at. The are only 2 other conductors going to the inverter are signals from the logic board, which I assume are on/off signals

    Thanks!
    Tags: None
    #2
    Re: Dell E171FPb No Backlight - Test Inverter?

    Clear focused pictures (2000x2000 max resolution) would help. Please upload the pictures using the manage attachments function and do not post line.

    If this is a Benq board, check the following

    1) picofuse to see if it is open
    2) c5707 transistors to see if they are shorted
    3) fu9024 fets to see if they are shorted
    4) you MUST resolder all the inverter transformer pins
    --- begin sig file ---

    If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

    We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

    Please do not post inline and offsite as they slow down the loading of pages.

    --- end sig file ---

    Comment

      #3
      Re: Dell E171FPb No Backlight - Test Inverter?

      Here is the best picture I could manage. It is an Ambit inverter board, so the BenQ stuff doesn't apply, though I did check the SMT fuse.
      Attached Files

      Comment

        #4
        Re: Dell E171FPb No Backlight - Test Inverter?

        I have limited experience of this model,but 25v to the Inverter PC seems unusual ??? hopefully someone on here know.

        Comment

          #5
          Re: Dell E171FPb No Backlight - Test Inverter?

          You really do not want to measure voltage at the CCFLs it will damage your DMM.
          The 25volts at the inverter is proably not excessive because ther is no load on the system.
          There are two pins at the conector of the Power supply, and the inverter.One is on/off, on alot of monitors this is about 3.3VDC when back lights are comanded on.
          There is also a dim pin this is usualy close to 0volts full brightness and a higher voltage for dimmer bulbs.
          Last edited by alexanna; 04-09-2011, 07:10 AM.
          Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

          Comment

            #6
            Re: Dell E171FPb No Backlight - Test Inverter?

            Thanks for the info Alexanna, that is helpful. Of the two "other" pins going to the inverter, one has 2.0VDC and the other 0V. A number of other pins on the logic board to power supply connector do have 3.2VDC, so I wonder if somehow the On signal to the Inverter is weak (corrosion, bad solder joint, etc). Dare I jump 3.2VDC from one of the other pins to the ON and see if the inverter fires up?


            All measurements were with the display on and an image on the screen.(

            Comment

              #7
              Re: Dell E171FPb No Backlight - Test Inverter?

              Originally posted by PBZ View Post
              Thanks for the info Alexanna, that is helpful. Of the two "other" pins going to the inverter, one has 2.0VDC and the other 0V. A number of other pins on the logic board to power supply connector do have 3.2VDC, so I wonder if somehow the On signal to the Inverter is weak (corrosion, bad solder joint, etc). Dare I jump 3.2VDC from one of the other pins to the ON and see if the inverter fires up?


              All measurements were with the display on and an image on the screen.(
              Here is what I would do, Check the voltages when the monitor is off.
              With a signal going to the monitor check the voltages again.
              Let the computer go into the sleep mode and recheck voltages.
              From on with a signal to going into a sleep mode one of the voltages should go low
              Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

              Comment

                #8
                Re: Dell E171FPb No Backlight - Test Inverter?

                Well I identified the On pin for the inverter (not the one with 2V, but the one with 0V, hence the inverter not turning on). By jumping this pin to 3.2V I can make the backlight come on at will. Since apparently this told me that logic board was not sending this signal for some reason I just decided just to wire in a manual switch for the backlight. While doing this I accidentally shorted between the On pin (which was also connected via a wire, to the pin on the PS supplying 3.2VDC to the logic board) and one of the pins that supplies power to the Inverter, and apparently there was still some juice in one of the capacitors, because I got a little spark.

                Well, no what was working before (everything but the backlight), is now not working. The logic board was not connected during any of this, so I'm guessing I fried something on the PS. The power to the inverter now reads at 35VDC, where it was reading around 25VDC before. Also the pin I was getting 3.2VDC from measures 0 with the logic board connected, though still 3.2 with it disconnected.

                Any Suggestions?

                Comment

                  #9
                  Re: Dell E171FPb No Backlight - Test Inverter?

                  Originally posted by PBZ View Post
                  Any Suggestions?
                  Yes, but you're not going to like it, If you shorted 25v to the BL on pin you really pissed off the inverter controller.
                  Honestly you have a problem on the logic board and now an issue with the inverter; I think it's time to salvage the good CCFLs for use in testing on future projects.
                  I would look for another monitor that's not working and attempt another repair.
                  Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                  Comment

                    #10
                    Re: Dell E171FPb No Backlight - Test Inverter?

                    The inverter actually still seems fine. With the Logic Board disconnected I can still fire up the backlights by jumping 3.2V to the On pin. I was assuming I damaged one of the other output sections of the power supply and this is why the logic board doesn't seem to be responding.

                    Comment

                      #11
                      Re: Dell E171FPb No Backlight - Test Inverter?

                      Does anyone out there have a schematic for the logic board OR the power supply in this unit, or perhaps even just the pinout for the connector between the two.

                      Knowing where to look for what supply voltages would be pretty helpful.

                      Comment

                        #12
                        Re: Dell E171FPb No Backlight - Test Inverter?

                        Me too my dell dont have backlight

                        Comment

                        Previous template Next
                        Working...
                        X